The influence of aluminium surface pretreatment on the corrosion stability and adhesion of powder polyester coating

One of the most important factors in corrosion prevention by protective coatings is the coating adhesion loss under environmental influence. Thus, adhesion strength is often used when characterizing protective properties of organic coatings on a metal substrate. In order to improve the adhesion of organic coating the metal substrate is often pretreated in some way. In this work, the adhesion of polyester coatings on differently pretreated aluminium surface (by anodizing, with and without sealing, by phosphating and by silane film deposition) was examined. The dry and wet adhesion of polyester coatings were measured by a direct pull-off standardized procedure, as well as indirectly by NMP test. It was shown that under dry test conditions all polyester coatings showed very good adhesion, but that aluminium surface pretreated by silane film showed superior adhesion. The overall increase of wet adhesion for polyester coating on aluminium pretreated by silane film was maintained throughout the whole investigated time period. The different trends in the change of adhesion of polyester coatings were observed for different aluminium pretreatments during exposure to the corrosive agent (3% NaCl solution). The highest adhesion reduction was obtained for polyester coating on aluminium pretreated with phosphate coating. The corrosion stability of polyester coated aluminium was investigated by electrochemical impedance spectroscopy in 3% NaCl solution. The results confirmed good protective properties of polyester coating on aluminium pretreated with silane film, i.e. greater values of pore resistance and smaller values of coating capacitance were obtained in respect to other protective systems, whereas charge-transfer resistance and double-layer capacitance were not measurable during 2 months of exposure to a corrosive agent.     

Synthesis and characterization of flexible polyester coatings for automotive pre-coated metal

An automotive pre-coated metal system has investigated to remove the wet coating process, such as pre-treatment, dip coating and spray coating for environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and formability to overcome the harsh conditions such as cutting, press and stamping process. For these reasons, flexible polyester coatings were designed to control flexibility using polycarbonatediol. The characteristics, curing behavior and viscoelastic property of the resins were measured by FT-IR, GPC, rheometer, DSC, RPT and DMA. The flexibility was evaluated using a texture analyzer. A nano-scratch tester, equipped optical microscope can measure the scratch resistance of coatings and the scratched surface morphology.With increasing polycarbonatediol content, the final frequency and the storage modulus increased and the T_g of the coatings decreased. This is related to the high mobility of the chain segment in polycarbonatediol. In terms of the flexibility and scratch resistance, CP-3 had high elongation value and good scratch resistance resulting from optimized stamping, pressing and cutting process in automotive pre-coated metal system. Therefore, polycarbonatediol is a powerful factor affecting the flexibility and scratch resistance of polyester coatings.     

UV固化不饱和聚酯树脂在涂料中的应用研究

以不饱和聚酯为光敏预聚物,加入光引发剂制得天然大理石表面紫外光固涂层(流水线作业)。研究了光引发剂用量对涂层性能的影响,并将UV固化与化学固化浇注体的力学性能和耐热性进行了对比。结果表明,紫外光固化不饱和聚酯树脂涂层的固化效果,硬度和亮度都达到化学固化的效果,且生产效率大大提高。     

The influence of Ce-based coatings as pretreatments on corrosion stability of top powder polyester coating on AA6060

Cerium-based conversion coatings (CeCCs) are one of the most prospective alternatives to the widely used chromate conversion coatings (CCCs) due to their anticorrosion efficiency, environmentally friendly nature and low cost. In this work, the CeCCs on AA6060 were prepared by immersion into aqueous cerium salt solutions at room temperature, and subsequently post-treated in heated phosphate solution. The effect of counter ion (nitrate and chloride) on the coating properties was studied testing CeCCs as sole or conversion layers for the top polyester coating. Since the 60 μm thick polyester coating was applied, an artificial defect of 0.8 mm hole was introduced to faster assess the differences between pretreatments. The system with CCC pretreatment was used as reference. Corrosion properties were investigated in 0.5 M NaCl solution by electrochemical impedance spectroscopy while the adhesion strength was measured by NMPR (N-methyl-2-pyrrolidone) and pull-off tests. As shown, the post-treated chloride-based CeCC offered better protection than crack-free thin nitrate-based CeCC, when used as sole coatings. On the other hand, it was brought to evidence that in combination with top powder polyester coating, the CeCC deposited from nitrate solution exhibited better protection compared to protective system pretreated with chloride-based one. Excellent polyester coating adhesion was found independently on aluminium surface pretreatment.     

Structure and properties of AlSi/polyester coating

Powder coatings, which are formed by plasma spray technique, are being used in industrial applications. Resistance of plastics and their based composite materials to chemicals, solvents, atmospheric conditions, and high impact strength even at low service temperature increases the importance of plastic and plastic based coating applications. In this study, aluminum silicon based polyester (AlSi/polyester) coating was applied by plasma spraying technique with and without intermediate bond layer coat (NiAl). The effect of coating thickness, intermediate bond layer coat, and plasma spraying parameters on bond strength of coating were studied experimentally. The bond strengths of the coatings were determined according to the ASTM C‐633–79. Microstructures of the coating were examined by optic microscopy and scanning electron microscopy (SEM), respectively. Obtained results indicated that plasma spraying current rate, coating thickness, and spraying distance were important factors on bond strength of coating. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2437–2444, 2004     

Degradation of polyester film in alkali solution

In recent years there has been a remarkable growth in coatings technology, yet polymer‐coated metals still corrode when they are exposed to severe environments. If the effectiveness of polymer coatings is to be increased, it is essential to understand the microstructure of polymer coating film and the changes that occur to the film upon environmental exposure, and relate the changes to the protective performance of coatings. The degradation of a polyester immersed in alkali solution has been investigated using a number of analytical techniques including atomic force microscopy (AFM), liquid chromatography/mass spectrometry (LC/MS), and Fourier transform infrared spectroscopy (FTIR). AFM was used to characterize the heterogeneous phase in the unexposed films and films exposed to alkali solution. Film roughness was found to increase with aging of the film in alkali medium. Total organic carbon analysis of the leached aqueous medium showed the presence of organic compounds, suggesting a chemical degradation of the film in alkali medium. FTIR analysis of the leached medium showed evidence for the formation of carboxylate species upon degradation of polyester film in alkali solution, while LC/MS analysis of the leached medium confirmed the presence of isophthalic acid and sodium isophthalate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2454–2463, 2000     

Effects of highly absorbing pigments on near infrared cured polyester/melamine coil coatings

In order to expand available colour range for an industrial coil coating line a range of 25 μm polyester melamine coatings were applied to galvanised steel substrate and rapidly cured using near infrared (NIR) radiative curing. The purpose was to improve understanding of this relatively new curing technology and identify any problems associated with differing absorption of a range of coloured coatings. It has been suggested that in order to increase efficiency of NIR cure, NIR absorbers should be added to the coating formulation. UV/Vis/NIR spectroscopy was used to deduce the parts that coating and substrate absorption play in topcoat cure and lab scale trials were run on coatings throughout the colour range with their heating profiles and surface finish being recorded and assessed. The results showed that in this particular application having a coating that absorbs too strongly in the NIR region can actually result in solvent boil defects due to cross linking and film formation occurring prior to solvent removal.     

Corrosion stability of polyester coatings on steel pretreated with different iron–phosphate coatings

The influence of steel surface pretreatment with different types of iron–phosphate coatings on the corrosion stability and adhesion characteristics of polyester coatings on steel was investigated. The phosphate coating was chemically deposited either from the simple novel plating bath, or with the addition of NaNO₂, as an accelerator in the plating bath. The morphology of phosphate coatings was investigated using atomic force microscopy (AFM). The corrosion stability of polyester coatings on steel pretreated by iron–phosphate coatings was investigated by electrochemical impedance spectroscopy (EIS) in 3% NaCl solution, while “dry” and “wet” adhesion were measured by a direct pull-off standardized procedure. It was shown that greater values of pore resistance, R_p, and smaller values of coating capacitance of polyester coating, C_c, on steel pretreated with iron–phosphate coating were obtained, as compared to polyester coating on steel phosphated with accelerator, and on the bare steel. The surface roughness of phosphate coating deposited on steel from the bath without accelerator is favorable in forming stronger bonds with polyester coating. Namely, the dry and wet adhesion measurements are in accordance with EIS measurements in 3% NaCl solution, i.e. lower adhesion values were obtained for polyester coating on steel phosphated with accelerator and on the bare steel, while the iron–phosphate pretreatment from the novel bath enhanced the adhesion of polyester coating on steel.     

Synthesis and characterization of elastomeric polyester coatings for automotive pre-coated metal

An automotive pre-coated metal system (PCM) has been investigated to replace wet coating process, such as pre-treatment, dip coating and spray coating, to address environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and stiffness to overcome harsh conditions such as cutting, press and stamping processes. For these reasons, elastomeric polyester coatings were designed to improve scratch resistance and to impart reflow characteristic for an automotive PCM. The characteristics, curing behavior and viscoelastic property of the resins were measured by ¹H NMR, GPC, RPT and DMA. The flexibility was evaluated using a texture analyzer. A nano scratch tester, equipped with an optical microscope was used to measure the scratch resistance of coatings and the scratched surface morphology. An Amtec laboratory car wash test and a sharp knife were used to evaluate the reflow property of the coatings. Change of the damaged surface morphology was measured using a mini-SEM.     

Synthesis of bio-based unsaturated polyester resins and their application in waterborne UV-curable coatings

In this paper, three bio-based unsaturated polyesters were synthesized from itaconic acid and different diols which could be derived from renewable resources. Their chemical structures were confirmed by FT-IR, ¹H NMR and acid value as well as hydroxyl value. Waterborne UV curable networks based on these polyesters were manufactured and their mechanical properties, thermal stability and coating properties including pencil hardness, flexibility, adhesion, water resistance and solvent resistance were investigated. Results showed that the UV-cured polyester coatings exhibited high hardness, good water resistance and solvent resistance. The coatings reported in this paper combined the merits of bio-based materials, UV-curing process and water distribution.     

有机硅改性聚酯的合成及其粉末涂料的性能

利用有机硅中间体合成了有机硅改性聚酯树脂。通过IR、GPC、SEM等分析了改性聚酯的结构与形态 ,用电子探针分析了改性聚酯的表面组成 ,考察了有机硅含量对改性树脂玻璃化温度、熔融黏度、对水的接触角及表面张力的影响。研究发现 ,改性聚酯中的含硅聚酯在表面富集 ,大大降低了聚酯树脂的表面张力 ,提高了其粉末涂料的涂膜耐候性。相对于纯聚酯树脂 ,有机硅质量分数为 1 %可使树脂的表面张力从 49.5降到 2 8.4mN/m ;经 2 1 6h中波紫外线照射后 ,涂膜的光泽保留率从 81 %上升到 91 .3 %。含有机硅质量分数超过 5 %后 ,涂膜的抗冲性能下降。     

Synthesis and characterization of acrylic-grafted polyester coatings for automotive pre-coated metal

An automotive pre-coated metal (PCM) system has been investigated to remove the wet coating process, such as pre-treatment, dip coating and spray coating for environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and stiffness to overcome the harsh conditions such as encountered in cutting, press and the stamping process. For these reasons, a series of acrylic-grafted polyester coatings (i.e., AGP-0, AGP-10, AGP-20, AGP-30) were designed to satisfy both the surface hardness and the formability for an automotive PCM. The characteristics of the resins were measured by GPC, FT-IR and ¹H NMR. The viscoelastic behavior and flexibility was evaluated using DMA and UTM. The physical properties such as pendulum hardness, pencil hardness and adhesion were measured to define the effect of incorporating acrylates. A cylindrical deep drawing tester was used to evaluate the formability of coatings.     

New polyester acrylate resins from palm oil for wood coating application

The aim of this study is to investigate the potential use of palm oil and to prepare new UV (ultraviolet) radiation‐curable acrylated polyester prepolymers, which could be used in the wood coating industry. Thus, palm oil‐based acrylated polyester resins PEPP‐1 (from refined, bleached, and deodorized palm oil) and PEPP‐2 (from crude palm oil) were synthesized at the Advanced Oleochemical Technology Centre (AOTC) laboratory of Palm Oil Research Institute of Malaysia (PORIM). The performances of these resins with respect to their curing rate and physical‐mechanical properties of cured products under UV radiation were studied. It can be concluded that newly synthesized UV radiation‐curable polyester acrylated prepolymers (palm oil based), namely PEPP‐1 and PEPP‐2, can be used as radiation curable coating materials for wood coating applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2156–2163, 2001     

An investigation of the effect of pigment on the degradation of a naturally weathered polyester coating

A series of coil coatings based on a polyester/melamine resin formulation, incorporating different pigment systems, were naturally weathered after being exposed to the elements in Hainan, PRC, for 2 years. The surface chemistry and morphology, before and after weathering, was investigated using both traditional (i.e., gloss retention, color change) and novel (i.e., X-ray photoelectron spectroscopy [XPS], atomic force microscopy [AFM], and scanning electron microscopy [SEM]) methods. Chemical changes occurring in the coating bulk were investigated using step-scan photoacoustic Fourier transform infrared spectroscopy (SSPA-FTIR). It was found that the coating surface morphology, surface chemistry, and bulk chemistry, both before and after weathering, were all affected by the type and concentration of the pigments included in the coating formulation. Moreover, it was found that different types of pigment catalyze different coating degradation mechanisms.     

Enzymatic hydrolysis of polyester based coatings

The potential of two hydrolytic enzymes, namely a lipase from Thermomyces lanuginosus (TlL) and a cutinase from Humicola insolens (HiC) for hydrolysis of the phthalic acid backbone based polyester coatings was assessed. Two phthalic acid/trimethylolpropane based model substrates resembling the structure of the polyester backbone of coatings were synthesized. Out of both enzymes, only the cutinase was able to hydrolyze both model substrates while the larger substrate was hydrolyzed at a lower rate. The cutinase was also able to hydrolyze a coating (alkyd resin) both in suspension and as dried film. LC–MS analysis of the hydrolysis products released from the coating revealed the presence of oleic acid, its monoglyceride, phthalic acid and 2-((3-((2-((2,3-dihydroxypropoxy)carbonyl)benzoyl)oxy)-2-hydroxypropoxy)carbonyl)benzoic acid. These results indicate that the enzyme was able to hydrolyze the polyester backbone as well as to release fatty acid side chains. Consequently, enzymatic hydrolysis has a potential for the removal of coatings, their recycling or their functionalization.     

Synthesis and characterization of silicone-modified polyester as a clearcoat for automotive pre-coated metals

Four types of silicone-modified polyester resins were synthesized for cleanable characteristics with silicone intermediate, which has a long chain, to extend the polymer chains of the resins. These resins were formulated to make polyester/melamine heat-cured coatings to control the formability. The characteristics, viscoelastic behavior and flexibility of the resins were measured by DMA and tensile test. The contact angle measurement can be measured by the water repellence of the coating surface, which is a standard method to evaluate cleanable characteristics. The surface free energy was calculated by the contact angle measurement, and the surface analysis of each cured coating was evaluated using an XPS. Silicone-modified polyester coatings were coated on the cold rolled steel sheets to verify their formability, using a deep drawing test. Results showed that the storage modulus decreased, and the glass transition temperature shifted to a lower temperature with increasing contents of silicone intermediate. So, silicone intermediate provides lower stiffness and higher softness to polyester coating. To analyze the formability, we calculated F_U (the forming coefficient based on strain energy) and F_? (the forming coefficient based on strain). When F_U and F_? are both larger than 1, the polyester coatings have good formability. CSiPE-3 and CSiPE-5 had good formability. Also, CSiPE-5, which had the highest amount of silicone intermediate, had 93.5° of water contact angle, and had 26.5 mN/m of surface free energy and had 5.5 N/25 mm of the peel strength. So, it is implied that silicone intermediate can give a low surface energy and peel strength to polyester coatings. From those tests, the polyester/melamine coating of CSiPE-5 that had 0.5 mol of silicone intermediate had good formability and low peel strength, which are semi-removable characteristics. So, it would be an appropriate coating as a clearcoat for automotive pre-coated metals.     

电弧喷涂与粉末涂料喷涂复合涂层防护技术

研究了热固性粉末涂料用作金属热喷涂涂层的封闭层及面层的防护技术,比较了分别喷涂环氧锌基重防腐粉末涂料、纯聚酯粉末涂料,喷涂环氧锌基重防腐粉末涂料后再喷涂纯聚酯粉末涂料以及热浸镀锌后喷涂纯聚酯粉末涂料等试样在不同盐雾和人工加速老化时间下的附着力.结果发现,只有熔融黏度偏低的环氧类粉末涂料适合用作封闭层.该复合涂层技术已应用于高速公路护栏上.     

On the electrochemical and structural behavior of biologically degraded automotive coatings; Part 1: Effect of natural and simulated bird droppings

Environmental factors can potentially deteriorate automotive coatings. These include UV radiation, humidity, hot–cold shocks as well as aggressive chemical compounds. In addition, natural occurring materials such as bird droppings and tree gums are also enable to affect the coatings. The present work aims to study the degradation of an automotive coating system exposed to natural and simulated bird droppings. To this end, structural analysis of samples was studied using FT-IR spectroscopy, optical and atomic force microscopes. Also, the mechanical and electrochemical behaviors of coatings were investigated by DMTA and electrochemical impedance spectroscopy (EIS). It was found that the biological materials significantly affect the mechanical and chemical properties of the coatings, resulting in a decrease in corrosion resistance. A two-time constant semicircle was observed for degraded coatings after a short time as a result of electrolyte diffusion into the coating/metal interface. The behavior of the coatings was then discussed based on the formation of surface defects.     

Degradation profiles of polyester–urethane (hydroxylated polyester/diphenylmethane diisocyanate) and polyester–melamine (hydroxylated polyester/hexamethoxymethylmelamine) coatings: An accelerated weathering study

The successful material performance of coatings depends on the environmental conditions to which they are exposed. The effects of the diol structure and acetoacetylation on the weathering degradation of hydroxylated polyester (HP)/hexamethoxymethylmelamine and HP/diphenylmethane diisocyanate clear coatings were studied. The acetoacetylation of HPs led to better performance for higher application solids than the acetoacetylation of their base counterparts. Weathering degradation profiles were investigated with dynamic mechanical thermal analysis, scanning electron microscopy, and X‐ray photoelectron spectroscopy. The structural variations of the building blocks and acetoacetylation were found to be important for enhancing the stability of coatings at higher application solids. Polyester–urethane coatings were more stable toward weathering than polyester–melamine coatings. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1069–1081, 2005     

Weathering degradation mechanism in polyester powder coatings

The replacement of terephthalic acid (TPA) by isophthalic acid (IPA), an isomer of TPA, in the polyester backbone produces a significant increase in the weathering resistance of powder coatings exposed to tropical climate. The study of weathering of IPA- and TPA-based powder coatings in accelerated weathering chamber has shown with support of FTIR spectroscopy, the formation of photo-byproducts that are proposed to be generated by a photo-induced oxidation converting –CH₂– in β-position to CO of esters into anhydride groups. Subsequent hydrolysis of these anhydrides is responsible of polymeric chain cleavage generating acidic groups and coating bleaching. FTIR analysis of exposed panels in Florida has demonstrated presence of same photo-byproducts.